Photoelectric conversion elements are used in various photosensors, copying machines, solar cells, and the like. These photoelectric conversion elements have adopted various systems to be put into use, such as elements utilizing metals, elements utilizing semiconductors, elements utilizing organic pigments or dyes, or combinations of these elements. Solar cells that make use of non-exhaustive solar energy do not necessitate fuels, and full-fledged practicalization of solar cells as an inexhaustible clean energy is being highly expected. Among these, research and development of silicon-based solar cells have long been in progress. Due partly to many countries' policy-wise considerations, dissemination of silicon-based solar cells is still in progress. However, silicon is an inorganic material, and has limitations per se in terms of throughput and molecular modification.
Under such circumstances, research is being vigorously carried out on dye-sensitized solar cells. Especially, to have built momentum toward such research is research results by Graetzel et al of École Polytechnique Fédérale de Lausanne in Switzerland. They employed a structure in which a dye formed from a ruthenium complex was fixed at the surface of a porous titanium oxide thin film, and realized a conversion efficiency that was comparable to that of amorphous silicon. Thus, the dye-sensitized solar cells instantly attracted the attention of researchers all over the world.
Patent Literature 1 describes a dye-sensitized photoelectric conversion element making use of semiconductor fine particles sensitized by a ruthenium complex dye, to which the foregoing technology has been applied. Further still toward the improvement of photoelectric conversion efficiency, development of ruthenium complex-based sensitizing dyes is being continued (see Patent Literature 2).